In what ways is the word “work” as used in everyday language the same as xbe( zcvms;ho. l kmcu4961y1that defined in physics? In wcy hles 1k1b .ox9m(;vz64cmuhat ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explain q ;u n92uwocoyhf1adq- 3s,1z.

Can the normal force on an ob)6kiy adn t1h93;s wcdject ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doiywak7do1 kn a 8q5xqf*7 h7.rmng any work? If shn7ak f q dwx517ro8.amqy*kh7 e stops swimming and merely floats, is work done on her?

Is the work done by kinerrq-y;; wer rd(r/d; wtic friction forces always negative? [Hint: Consider what happenswddr yr;qr;r/(we-; r to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though yo fq65j3 ;fpyaqu are doing no work?f536py fqqja ;

You have two springs that are identical except that spring l is stiffer t77r xka2p4:hrjqv h :d4/-cix g-x lmyhan sprinr 7jgmd iy:4x ahhc :plx-2qx7-4k/r vg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant ho 2r;xe9l);(ybov8ie he 12ri q muz;xrrizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by tir8z9; r;q e)e(yxxr21lu; vomib h2ehe time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy oz3cy2(uy:a 5)c09i mwlnsx tchange when yow9oyut0:)nma5 c3yxsil(2cz u jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all witi10d ri.v/khylxua-: d;,o v oh the ilvxoy k;1hi- odu.dr0:,/vasame speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height . jng6l rorrkm1 +i,e2h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is dire6kre2jmr.lr+no , 1ig cted upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you)wjvlp5g sn7x, g/ oyl 2-oul; compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law oo- x)w5v l72u/gg;ysn llo pj,f conservation of energy.

A bowling ball is hung from 4zx2 /jubldr.3 xw6f3cy;vnx the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avo2rzxfw x6/b4d.3 ;jn 3vcluyx id injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watjf.v8 h+6nmin 99pn;- xhp1it ikbvi4 er at the top of a waterfall falls to the pool below+mb8vfvix9nki6 hj1nn9 h 4-;i. tppi?

Describe the energy transformations when66m4g k7c.f ncx-r5t /uj q+dhovjc;y a child hops around on a pogo stick.

Describe the energy transformations thatm; d oo z*g-j96c8yydj take place when a skier starts skiing down a h-9mg o6cjy;yzd jd8*o ill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heu o9yvsomb k9(ov9e8 6ight h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy aok ubevo 9y9osvm 9(86nd there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rat rxme6;dp qiuv mb9dm c7;+-.bher than stepping on top a7u bm rp9dm mq e6xic-;d;+.vbnd jumping down on the other side. Explain.

Two identical arrows, one with twijg kidd;/ :;yp 3en;woce the speed of the other, are fired into a bale ofkgi;; ; djpdyon: /e3w hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendul elmot 4+b:kom6wdb-+-/ t gqgum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has toml-qo+mtb -t: dg+/ 6ge wb4ok be wound up.

When a “superball” is dropped, cant*c -0bv w(z6pv il9,l5wqr5b z.3;buuvwffs it rebound to a height greater than its originlw vtup-53iql6cs5u v0wb;z.rw fv *bb9fz , (al height? Explain.

Suppose you lift a suitcase from the floor to a tt:4hhv o:,g de9cqa4 59sl woxable. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) thel s:4hd5e9ah9ot:qc x 4gwo, v height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather t qzr0g3 ofo.f) v*en)jgqnmbnw/ g82/han the work.

Why is it easier to climb a mountain via a zigzag trail than toac9 fzx 8o*v2h9: kjqf climb straight ukjfhofaqv:8 z 9*92cx p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to d t0mb29zi(i n jnu(2mvigb,-mecrease the force needed to raise a (n 0, 9mmiz mjvigb(t22iunb -heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile +, uvdwd5*tux driver fallsd xtu5v,+u *wd 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of sp60jvcc) x i8dtairs 20.0 m high. How much work is required8vx)dc0 pcj 6i?    J

  A 1300-N crate rests on the flo3p+w ,wl20woz3tdx v t17lpdx or. How much work is required to move it at constant speed (a) 4.0 1p0tw+ 3d zxo3vtl,2w d plw7xm along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hou uwlqz6 ;e*o7 ),kbyurizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wuu;6bkq y7eu oz, *l)was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force ge;j;qjx-3j whbci8i, ,8 mqk across a floor at a rate of for 7qiek;j wj;38j gbci8, -xhmq,.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass y0a (99fe bfc ha0 gx3gmbxy-81.7 kg, lie flat on a table. How much work is required to stack them one on top of an(- 0 chmf3fgby9a90b8ygxxa eother?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we c-y f/ky y-m0tmight not otherwise be able to liff. Show that the ratio off0/y- t-kmyy c output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelea *15gj )t(j)dsgwu mbrating by a )utm)*jajg d(1gwb5s man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleration 8 mpe6sptfi1:l58ye 3 hq1tcb i 06zcqof 0.10 g upward. yqc0f65:s8e th 31 mi1 lptq c8be6piz   Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume trz:m80p2 fe vshe distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies c,ug6 w9lwhx7 as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0luw,c9wgx 7h6 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts k2izvkb3v)3n lu+*u fin the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecm ib al kpg 86)as+))bj,2lvnzule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed increas jua9p7v g1r5ikb+pq5q)o q :eed? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electro2:pk qay( 4llf 4/ijaln $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop ac. 8amwu fn;:b 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firelcdbghha5453 . os7 ;qogrs0 nr9i q3md from a bow whose string exerts an average force of 110 N on the arrow over a distahgima9g7 rr5 s q.53ocn4osqlhb 3d0 ;nce of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mornm(knt z2 c t*/tjorsoc92g-*a0xo* ves a fielder’s glove backward 25 cm when the ball is caught. What wacxrno0ko - snr**m2/ca tg2tz(j to*9s the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50 8k*d*g2c-s b(zhq 1osy)vc jz%, by what factor will its minimum brakinjy *cg)qc8 o1 z(b2-hk zs*sdvg distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators) hk mfb,.(bdd measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locke().b k,bdmdf hd) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.2.g qhc(+. y cw:p,tjek5 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting (wyqg, h+c.kpj.:ce tgravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rd d:5m:yr- ajt7jg.vxz a8x 6fock go if thrown straight up by someone who does 80.0 J of-yxt85gj 7fj6:x rzm .aadv:d work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 8azhnx/ g4-/k bys ,aqm vertically with an acceleration by a single cable. Determinbk y4/qn8hg ,s-a/ zxae
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this sprips*t -ad,.dq j ,-atrtng be stretched to storej *-dats.a,q ,ptdt -r 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 1k .u-cxi4xzdr4 b.; o :gp3zp /dnyajm higher. What is the change in potentiapgk 3zpj-nbza1;i4/. yodur:xd .c4 xl energy?    J

  By how much does the gravitational potential energy of a 64-kg pole 5o)qn5b1hjumzh5 m s9vaulter change if his center of mass rises about 4.0 m during the j)nm h5hz91 ubo s55qmjump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it u/flt0;3fw+ecng.j; 8to os y strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. wfcltyg /o;8tfn 3u;e.+ojs 0What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book f+ 4zxxiq7yn2 k1w7gc3ox c v)n,kl f9orom the ground so it is 2.20 m above the ground. What is the pote 9ox14nk )wo3f7vn 7q ckcz+2iygl,xxntial energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to ther3a3bb05 h*izxyn( ot top of a 3300-m peakb0 haz(3 rn5oti*xb y3.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next tq)gof zqr 1 n;lr -tbc3+m8fj1m1d fi*o a ruler. The end of the spring is next to the 15-cm mark ojq1tmgq i+ln;bfm*r)f3of z-d c 181rn the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runningrn k b)bih:.d406ds8a:zt q kdqt -9 wvcxp6q, at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing uph9z-vd: x6,40 wtq6crdi: skpkn )8tbqab dq .ward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting f7 )zq 4n 8ylv;kdub2qguhr7g1rom rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frt3 ;csnj,hh0 hictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transmv3bhiuw,(/h1 reg 4gformed into gravitational potential 1 g3vhwhiu(reg/b, 4menergy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artislq8 ie02iow f9-4djxy b9dk*,my(o kzt jumps vertically upward from the top of a platform with a speez9w(y9d,koeyxi4o l -ijdkf0*8 b2q md of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose hmjmmwx4ut1gp47u8ai9en*+y6a p 6a spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it giveu 9m8ju4hxpy mnme1wag*pt 76 a 6i+4a to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without frictirpf6ey(d nn5agl .e+0on along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the to y. a lr0dnepgn+(5ef6p of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness co4m 7fsb4qk nr2nstant k), Fig. 6–40. The block is given an initial displacementmk24q7n 4 rbfs $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridgp;v izln*1jlg * t4ro;e. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming ;p 1gv to4rin;j*l*zl Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dporb0 *vvjpj:,8yg 0g ragged up to point 1 where it is released from rest. Assuming no friction vgbg0 :v p,jpo8rj*y0, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/ unlc f)nd/2y 6y.mqg3s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designingpr07-w4 ykvwvgsm7 )cwf,u z5 a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevatoku5c7-mzwy sp7,rfwvv) 4g w 0r and passengers.

  A cyclist intends to cyc orcfc-g1/ *ccle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in o3wg(e6e e3l qry a+ cey3mk m*cqv,(0lpposite directions, collide head-on and come to rest. How much thermal energy is produced in this cg3(3qcq6 0ywerk em(*e ml 3el+yv,acollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high 6(n,t gry.hv kand reaches the bottom with a speed of 2.2m/s How muc( g.6t nyvh,krh thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slin(ov p8syh +zx+up 7)odes down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped 9b 1l*o psxmllsun/.)from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2z58(:cjqn n g+1cpba9ik c) pm.0 m, and it bounces back to a height of 1.5 mjq: nbpmc+95)cn g c(zkp1i a8.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant ho-iv -xnw 2 dc1vd0ay 4/swm(gtrizontal force of 350 N. For the first 15 m the floor is frictionless, 01i -dy/x4 (a2mdnw vst gcwv-and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speegvpc-6 w dq/y,mf 7f:gd of If the average force of friction is equal to one-fifth of its weighpfm-:qd, f /vc6wyg 7gt, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0 /m39d5v8wdpz uj(n zk$^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very lightzp6v .uekr hlsr) i+66 horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium positep6+irk6 hzru ls. 6v)ion before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sx u4gem4md-+gh 1tiq wg2c(,zpring, Fig. 6–40. The block can slide along a table where the coefficient w2hx(u4ggcgz4 ,mq +d-mt1ei of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the 6fegi an+sdhf2hzezn 0r 21 54space shuttle used a “glider” (mass of 980 kg including pilot) n5nseaefz42f2 r+ h1 gzi6dh0 that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-stor 7 +dfzy;ow nj5ljx;:8 -dl1der,xchm y window 16.0 rhxld-xmd:+jw zf1c57e;;ln 8y, djo m above?    s

  If a car generates 18 hp when traveling aqme 7r bhn37pwmp,n/.t a steady 88km/h what must be the average force exerted on the car due to friction and air r7emh qp mw7b3rp.,n/nesistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the16aetd ye4 fc9 average power delivered by the engif1ae6e dct9 y4ne?$\approx$    hp

  (a) Show that one British horse8 j;s)ls a/xt,zv3 ;jebgbt8o power$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are o rbz0slu:w0p;kd 8r+z//ommv ften expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her - urx5l- i.xxcgx1ua 61150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling a -.xl-ixc gx61ru5xu at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do i:q7quyw7vb b3b847 xjjemv+ en 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg 1 pf;w7a9 yrsn45pt( wg)kinwshot from rest to 14m/s If this motion takes 1.5 s, what average power was1n4kstiwf )ppwn( wr 57g;a 9y developed?$\approx$    W

  A pump is to lift 18.0 kg ofu z*(it yos3;c:ofcg; water per minute through a height of 3.60 m. What output rating (watts) should the pumpc(ozg*u;tycis o; f:3 motor have?    W

  During a workout, the football players at State U. ran up the stadiume4xav:w yrv+3 stairs in 66 s. wy4:r+3 vvaxeThe stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclis1qp*:4 az zz.bgxgga 2u+u r9at climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a s) :z/.fmtgi qmaximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up t qf)z:s.i/t gmo 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be abyguopm-5u sa4 .qd.4ole to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictionopm gqy-usoa4d. 4.5u is 0.45?    hp

  A bicyclist coasts down a 7.0 pbbt9vyw. u84x. 2wfb$^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8k osn1jmpi j k032i3y;lm/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a coop 3imikj3jsn 1 y2;l0mpression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remain xzh h(fzg04l*p) pgb*ing four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and a x0b*f(ghlhp* zz4pg) n average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig.1ik:xje/f6*6* s (uobxu ksjp 6–42) in the 1936 Olympics shows that his center ou(6fbpxux/es*jk ks6o1 :j i *f mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the 184 mmr q8 kwt* ol;rbqt,ku;zlooped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r. ,m;*8mq wkl8 1tqt r k;orzu4b
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jubo 43umnsls73o0kj +mb6 vq+dmping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, butovjs4n70kbd q6m+ 3 +obms u3l survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is rd 9(;4p qkouv+v6z 2lsix 3hn7-atwz fixed (Fig. 6v 4;xo+lh pik t(62u-3qdvs9z7wznra –43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is mad +/3zmi feifb0e in 5.0 h starting atemb0f/3+i ifz an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a a5b89g95,b 6-zi jrvv7 ozssire;upi 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,7dkas /bo7+ yd+/ecl d000 people per hour /+k 77l+deaoybdcs/d . If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls f9uo:q q j)+.yvmh( gomp6s0. o pdln/vertically 81 m before striking the turbine blades. Calculam6.qg p +pm)qysoo ujv:9n/hdo lf.0(te
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), thew3m:luzgm 5syco(o.z7tat n.znd n, , +-zrt 5 difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6w,z.7rm,t:n5-u z .(ly5 o+ cd zgno ttsmnz3a g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert aahpdr9c05):d9 ung,q z c6ady+s tf7p candy bar directly into work, how high could an 82-krz9 0 q5cgdun+pd h6c97y:da),pfastg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwardoo/m o,yt yhyv/,k1*ou c)zk0 angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the sprinov: p)scp(dfr0( h, vlg inside the scale compresses 0.60 mm, and it tells you your weight is 710 N.hr(dosf(v0c ) p:, plv Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. d km a5k lso2,*(f5bs eifm42d6–45). He releases the rope when his velocity is zerolssk5fm2i*f 4kbed a5o2d ,(m .
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical d46higgf9 djz *(pb egk3v4rl 5istance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat ggj4vlez95 3p*ibgdf4hr6k (?    W

  Some electric-power companies2hz1sl lb w.q26x/ohl use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the en/ol wsxh ql1226.blzhergy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spring 4w3psm e+jh d7stiffness constant for each of the two resulting springs? ms7dh4jew3+ p  k

  A 6.0-kg block is pushed 8.0 m up a rouok0ajnzz cs*1*ux, ; agh 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s0lkye/ hv iu4 ,5)yghv/w2k 0jvrq)dd , how long will it take to accelerate f5yhg4 v)2ljidy u he qwvk0,)dv0 rk//rom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stres f fqp42hb4ln3s test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whenffln3 hp q42b4 the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m, wr/u -7,gm4sv yx:isw o0g 7rvphatoi7r04rsx v/ :vs- gu mpy,w7g was its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from (+gg j9zbdcmzs03g0z a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity outg(0jg3mz+ b c9szd0 gzput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s